Field of the Invention
The present invention relates to an internal combustion engine.
Discussion of the Background
Regarding internal combustion engines, there is a known technique in which blow-by gas leaking from a cylinder into a crankcase is returned to an intake passage and is mixed with fresh air for combustion (see Japanese Unexamined Patent Application Publication No. 2006-194108, for example). In an internal combustion engine disclosed by Japanese Unexamined Patent Application Publication No. 2006-194108, a crankcase and a portion of an intake passage that is on the downstream side with respect to a throttle valve are connected to each other with a reflux passage. In the downstream portion of the intake passage, which is subject to an intake negative pressure generated by the reciprocating motion of a piston, the pressure is relatively lower than that in the crankcase. Therefore, blow-by gas flows from the crankcase into the intake passage. The reflux passage is provided with a one-way valve (a positive-crankcase-ventilation (PCV) valve) that allows a fluid to flow only from the crankcase toward the intake passage.